body {
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  height: 100vh;
  background: linear-gradient(#141e30, #243b55);
}

.login-box {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 400px;
  padding: 40px;
  transform: translate(-50%, -50%);
  background: rgba(0, 0, 0, 50%);
  box-sizing: border-box;
  box-shadow: 0 15px 25px rgba(0, 0, 0, 60%);
  border-radius: 10px;

  h2 {
    margin: 0 0 30px;
    padding: 0;
    color: #fff;
    text-align: center;
  }

  .user-box {
    position: relative;

    input {
      width: 100%;
      padding: 10px 0;
      font-size: 16px;
      color: #fff;
      margin-bottom: 30px;
      border: none;
      border-bottom: 1px solid #fff;
      outline: none;
      background: transparent;

      &:focus ~ label,
      &:valid ~ label {
        top: -20px;
        left: 0;
        color: #03e9f4;
        font-size: 12px;
      }
    }

    label {
      position: absolute;
      top: 0;
      left: 0;
      padding: 10px 0;
      font-size: 16px;
      color: #fff;
      pointer-events: none;
      transition: 0.5s;
    }
  }

  a {
    position: relative;
    display: inline-block;
    padding: 10px 0;
    color: #03e9f4;
    font-size: 16px;
    text-decoration: none;
    text-transform: uppercase;
    overflow: hidden;
    transition: 0.5s;
    margin-top: 40px;
    letter-spacing: 4px;
    width: 100%;
    text-align: center;

    &:hover {
      background: #03e9f4;
      color: #fff;
      border-radius: 5px;
      box-shadow:
        0 0 5px #03e9f4,
        0 0 25px #03e9f4,
        0 0 50px #03e9f4,
        0 0 100px #03e9f4;
    }

    span {
      position: absolute;
      display: block;
      text-align: center;

      &:nth-child(1) {
        top: 0;
        left: -100%;
        width: 100%;
        height: 2px;
        background: linear-gradient(90deg, transparent, #03e9f4);
        animation: btn-anim1 1s linear infinite;
      }

      &:nth-child(2) {
        top: -100%;
        right: 0;
        width: 2px;
        height: 100%;
        background: linear-gradient(180deg, transparent, #03e9f4);
        animation: btn-anim2 1s linear infinite;
        animation-delay: 0.25s;
      }

      &:nth-child(3) {
        bottom: 0;
        right: -100%;
        width: 100%;
        height: 2px;
        background: linear-gradient(270deg, transparent, #03e9f4);
        animation: btn-anim3 1s linear infinite;
        animation-delay: 0.5s;
      }

      &:nth-child(4) {
        bottom: -100%;
        left: 0;
        width: 2px;
        height: 100%;
        background: linear-gradient(360deg, transparent, #03e9f4);
        animation: btn-anim4 1s linear infinite;
        animation-delay: 0.75s;
      }
    }
  }
}

@keyframes btn-anim1 {
  0% {
    left: -100%;
  }

  50%,
  100% {
    left: 100%;
  }
}

@keyframes btn-anim2 {
  0% {
    top: -100%;
  }

  50%,
  100% {
    top: 100%;
  }
}

@keyframes btn-anim3 {
  0% {
    right: -100%;
  }

  50%,
  100% {
    right: 100%;
  }
}

@keyframes btn-anim4 {
  0% {
    bottom: -100%;
  }

  50%,
  100% {
    bottom: 100%;
  }
}
